31 C.F.R. § 306.128
Supplements, amendments or revisions
The Secretary of the Treasury may at any time, or from time to time, prescribe additional supplemental, amendatory or revised regulations with respect to U.S. securities. The Secretary also may lower the minimum and multiple requirements for stripping marketable Treasury notes and bonds issued prior to March 1, 1993, through an announcement as provided in § 356.31 of this title.